134 THE PRINCIPLES OF FLORICULTURE 



so that cross walls form and the original cell becomes 

 divided into many cells. This process of division brings 

 more or less pressure on the cell walls, causing them to 

 assume various forms. In the higher types of plant life, 

 these differently formed cells function in various capaci- 

 ties. Some serve to absorb food contents, and some to 

 conduct food to other cells. These, in turn, have the 

 power of changing crude food substances, as they are 

 taken into the plant, into material which becomes a part 

 of the protoplasm, therefore building up plant tissue. 

 Individual cells often become elongated, and are shaped 

 like rigid or flexible tubes. 



As a plant matures the cell-contents change, and the 

 protoplasm passes out from the older cells. The cell 

 walls, however, remain and form the bulk of the individual. 

 These cells are for the most part in the center of the plants ; 

 for example, the heart-wood of a tree. The vital, active 

 cells are mostly near the outside where they are in direct 

 communication with the oxygen of the air. Most plants 

 have a more or less thickly developed outer covering, which 

 is generally termed the bark, and from this bark dead 

 cells are constantly falling off. 



106. Cell names and their location. The following 

 are among the most common special cells with which the 

 plant grower should be familiar : 



Cells of the root and stem. 



(a) Root-hairs. Root-hairs are more or less elongated, 

 epidermal cells which are found on or near the 

 tips of all living roots. They are mostly micro- 

 scopic, but may be seen with the naked eye on 

 roots of large seedlings germinated in sawdust 

 (corn, bean). 



